This invention relates to an air conditioning control system for automotive vehicles, and more particularly to a system of this kind which has a compressor having capacity thereof controlled at the start of the compressor such that almost no shock is caused by the engine of the automotive vehicle upon engagement of the compressor clutch.
A conventional air conditioning control system for automotive vehicles in general has a compressor forming part of the refrigerating cycle, which is driven by an engine installed in the automotive vehicle, through an electromagnetic clutch. However, immediately when the electromagnetic clutch is brought into engagement to connect the compressor to the engine, a shock is caused by the engine due to a sudden change in torque transmitted from the engine, causing discomfort to the occupant of the vehicle.
In order to prevent such shock, an air conditioning control system for automotive vehicles has been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 63-184519, in which a compressor has a pressure control valve arranged therein for leaking pressure within the crank chamber into the low pressure or suction chamber, and a control unit for supplying a control signal (control current) to the pressure control valve for varying the the pressure within the crank chamber and hence the capacity of the compressor.
According to the proposed air conditioning control system, the control signal from the control unit is set to such a large current value as to bring the compressor capacity to the minimum capacity upon engagement of the clutch at the start of the compressor, and thereafter progressively increased to a predetermined current value so as to progressively decrease the pressure within the crank chamber until the compressor capacity increases a predetermined capacity.
However, in the case where the air conditioning control system employs a variable capacity compressor of a wobble plate type which has capacity thereof controlled such that the suction pressure of the compressor is controlled to a predetermined desired value, the capacity actually varies in the following manner: Even if the control signal is set to such a large current value as to bring the capacity to the minimum capacity at the start of the compressor, the pressure control valve is forced to open by suddenly increased pressure within the crank chamber upon starting of the compressor, to leak pressure within the crank chamber into the suction chamber. Consequently, the pressure within the crank case suddenly drops, so that the actual capacity is suddenly increased to the maximum value (instead of being progressively increased) by reduced pressure within the crank chamber. After thus suddenly reaching the maximum value, the actual capacity is progressively decreased to the minimum value, as the pressure within the crank chamber is increased by the control signal. However, it takes at least 10 to 20 seconds to bring the capacity to the minimum value from the start of the compressor.
Therefore, the proposed air conditioning control system had the disadvantage that the shock caused upon starting of the compressor is difficult to reduce, and further such shock in turn results in poor driveability of the engine particularly during idling operation.